Cardiovascular disease is a major health risk throughout the industrialized world. Atherosclerosis, the most prevalent of cardiovascular diseases, is the principal cause of heart attack, and stroke, and thereby the principal cause of death in the United States.
Atherosclerosis is a complex disease involving many cell types and molecular factors (for a detailed review, see Ross, Nature, 362(80):1-809 (1993)). Results from epidemiologic studies have clearly established an inverse relationship between levels of high density lipoprotein (HDL), which transports endogenous cholesterol from tissues to the liver as well as mediating selective cholesteryl ester delivery to steroidogenic tissues, and the risk for atherosclerosis (Gordon et al., N Engl. J. Med., 321:1311-1316 (1989)).
The metabolism of HDL is influenced by several members of the triacylglycerol (TG) lipase family of proteins, which hydrolyze triglycerides, phospholipids, and cholesteryl esters, generating fatty acids to facilitate intestinal absorption, energy production, or storage. Of the TG lipases, lipoprotein lipase (LPL) influences the metabolism of HDL cholesterol by hydrolyzing triglycerides in triglyceride-rich lipoproteins, resulting in the transfer of lipids and apolipoproteins to HDL and is responsible for hydrolyzing chylomicron and very low density lipoprotein (VLDL) in muscle and adipose tissues. Hepatic lipase (HL) hydrolyzes HDL triglyceride and phospholipids, generating smaller, lipid-depleted HDL particles, and plays a role in the uptake of HDL cholesterol (Jin et al., Trends Endocrinol. Metab., 13:174-178 (2002); Wong et al., J. Lipid Res., 43:993-999 (2002)). Endothelial lipase (also known as EDL, EL, LIPG, endothelial-derived lipase, and endothelial cell-derived lipase) is synthesized in endothelial cells, a characteristic that distinguishes it from the other members of the family.
Recombinant endothelial lipase protein has substantial phospholipase activity but has been reported to have less hydrolytic activity toward triglyceride lipids (Hirata et al., J. Biol. Chem., 274:14170-14175 (1999); Jaye et al., Nat. Genet., 21:424-428 (1999)). However, endothelial lipase does exhibit triglyceride lipase activity ex vivo in addition to its HDL phospholipase activity, and endothelial lipase was found to hydrolyze HDL more efficiently than other lipoproteins (McCoy et al., J. Lipid Res., 43:921-929 (2002)). Overexpression of the human endothelial lipase gene in the livers of mice markedly reduces plasma concentrations of HDL cholesterol and its major protein apolipoprotein A-I (apoA-I) (Jaye et al., Nat. Genet., 21:424-428 (1999)).
Various types of compounds have been reported to modulate the expression of endothelial lipase, for example, 3-oxo-1,3-dihydro-indazole-2-carboxamides (WO 2004/093872, US 2006/0211755A1), 3-oxo-3-H-benzo[d]isoxazole-2-carboxamides (WO 2004/094393, U.S. Pat. No. 7,217,727), and benzisothiazol-3-one-2-carboxamides (WO 2004/094394, U.S. Pat. No. 7,595,403) by Eli Lilly & Co.; diacylindazole derivatives (WO 2007/042178, US 2008/0287448A1) and imidazopyridin-2-one derivatives (WO 2007/110215, US 2009/0076068A1), and azolopyridin-3-one derivatives (WO 2007/110216, US 2009/0054478A1) by Sanofi-Aventis; heterocyclic derivatives (WO 2009/123164) and keto-amide derivatives (WO 2009/133834) by Shionogi & Co., Ltd. However, because endothelial lipase is a relatively new member in the lipase gene family, a full understanding of the potential of endothelial lipase inhibitors to human health, as well as the inhibitors of other lipases in general, requires more studies.
Thus, there is a clear need for new types of compounds capable of inhibiting the activity of lipases, particularly endothelial lipase, that would constitute effective treatments to the diseases or disorders associated with the activity of such lipases.